The characteristics of cenozoic sedimentary basins in the North China platform

Abstract

In the Cenozoic, a series of faulted, downwarped basins developed in the North China Platform. The large depressions located in the eastern part of China are the North China Depression and the northern Jiangsu Depression. The depressions are comprised of a series of parallel grabens (mainly single-fault grabens) and uplifts. In the central part and along western and northwestern margins of the North China Platform, there is a series of smaller en echelon grabens. These depressions and grabens formed during Late Cretaceous, Early Paleogene and Early Neogene. Formation and development of the grabens was controlled by tensional normal faults, characterized by steep dip in the upper parts and gentle dip in the lower parts of the fault planes. The Cenozoic sedimentary fill of the large depressions differs from the smaller grabens. The large depressions are filled mainly by paralic lake sediments which are the most important oil-producing beds in the Cenozoic of the eastern part of China. As sea water intermittently invaded the depressions, many so-called abnormal marine beds were deposited. The sedimentary sequences were intruded by alkali-basalts and tholeiites. In contrast, in the smaller grabens mainly lake-river sediments were deposited. The Cenozoic paleoclimate record for the North China Platform shows that a sub-tropical, warm-humid climate prevailed in the Paleogene, followed by a warm-dry climate in the Neogene and by temperate cold-dry to cold, humid climate in the Quaternary. The tectonic evolution of the two-large depressions can be subdivided into two stages: (1) the faulting stage of Late Cretaceous to Paleogene, when series of parallel grabens and uplifts were formed; and (2) the downwarping stage (Neogene to Quaternary) when two large depressions were formed. The formation and evolution of the Cenozoic depressions and grabens of the North China Platform was influenced by extension and faulting of the crust resulting from uplift of the upper mantle.